Have a 15.5 HP B&S on an early 2000's craftsman rider. Last year was difficult to start, this spring, impossible. When turning over, it hits a spot where it just can't go further with the starter. Have replaced starter, solenoid, battery, plug, and adjusted valves (which move freely-I have had the head off as well). If I hold the lever that operates the compression release ("easy starting" mechanism), then it turns over really well, but won't start. As soon as I begin to ease the lever into the position it should be in, the motor backfires through the carb and exhaust really badly, and becomes unable to turn over again. Obviously it has something to do with a timing problem or a compression-release problem, but I can't figure it out.
15.5 B&S mower motor troubles...
- Thread starter dcmcclain
- Start date
It is located near the rear of the motor, very close to the bottom. It is connected by a lever to the throttle. When I push the throttle up far enough, the throttle mechanism that is connected to the carb pushes this lever a bit.
That is the governor control arm. When you push on it you are opening the throttle. I think you have a fuel problem. Spray a little carb cleaner into the airhorn with the throttle wide open. It should fire butnmay not run. Let us know.
Thanks, I forgot to mention that I have had the flywheel off to check things out in there, no problems. It sure is acting like it's out of time somehow, though.
Just tried to "prime" the thing. Problem is, it is simply too hard to turn over. When I turn the key, the flywheel turns just so far, then the compression is too hard for it to keep going. Once in a great while, it will fire, and when it does, it is through the carb or the exhaust.
By the other posts I have seen with similar problems, it sure seems like I have eliminated everything except a bad cam.
Thoughts?
Just tried to "prime" the thing. Problem is, it is simply too hard to turn over. When I turn the key, the flywheel turns just so far, then the compression is too hard for it to keep going. Once in a great while, it will fire, and when it does, it is through the carb or the exhaust.
By the other posts I have seen with similar problems, it sure seems like I have eliminated everything except a bad cam.
Thoughts?
OzRanga
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Take the rocker cover off and check the following...as process of elimanation:
Ensure both rockers are operating about the same (there was a bad batch of cam lobes wearing at one stage but unlikely). This will also check any bent or broken pushrods
Check the bottom rocker is opening the inlet valve ever so slightly on the compression stroke (opens valve only a thou or two)
Double check valve clearance on both valves is at 0.003-0.005" with piston 1/4" past TDC on power stroke.
Let us all know what you find with the above
Ensure both rockers are operating about the same (there was a bad batch of cam lobes wearing at one stage but unlikely). This will also check any bent or broken pushrods
Check the bottom rocker is opening the inlet valve ever so slightly on the compression stroke (opens valve only a thou or two)
Double check valve clearance on both valves is at 0.003-0.005" with piston 1/4" past TDC on power stroke.
Let us all know what you find with the above
At least I know that I was on the right track at one point here. I have checked the push rods, they are fine, and the valves open both the same. I have set the valve clearance to .005" on both. I just tried determining with a feeler guage whether the lower valve is opening on compression stroke. It seems like it is not.
From you description I would say that the compression release on the camshaft is broke and will require a new cam to be installed. Have one in the shop right now where the flyweight on the camshaft broke and was lying in the oil pan.
This is my first time this deep into a small engine. What is the flyweight? I have completely disassembled the motor. On the cam, the little lever still has a spring around it, but it doesn't look like it would do anything. I found pieces of metal in the pan and all over inside the crankcase. Some are small, but several are quite large, like 1/8" thick and 1/2" long, look like a piece of a large, tapered washer or something. It is cast metal, and is not aluminum. I have inspected all the parts inside that are cast metal, and none are damaged. It has to be something that is so damaged it is unrecognizable and missing from wherever it is supposed to be.